Dry toner has been mainly used in image forming apparatuses such as copiers and laser printers, which are prevalent in the market. These image forming apparatuses employ electrophotographic-processes (i.e., an electrostatic latent image formed on a photosensitive plate including a photosensitive layer is developed with toner grains). An image forming apparatus that uses toner only for a developer has a toner cartridge, which comprises a toner hopper for accommodating toner, and a toner-fine-layer-forming-section that forms a fine layer of tribo-electrically charged toner on a developer roll.
The toner in this toner hopper is supplied to a toner-replenishing-roll by a toner transporting member. The supplied toner is transported to the developer roller with friction between the developer roll and the toner roll. The toner, which arrives at the developer roll, is charged by friction between the developer roll and a doctor blade, and thereby forms a fine layer on the developer roll. Part of the fine layer is consumed to develop an electrostatic latent image formed on the photosensitive plate, and the remaining toner is returned to the hopper via a PET (polyethylene terephtalate) sheet and the developer roll.
The toner flow thus generally falls into three categories, i.e., (1) circulating within the hopper to prevent the toner from being solidified, (2) developing electrostatic latent images, and (3) unused toner for the developing. The grain size of nonmagnetic toner filled in the cartridge ranges from ca. 2 .mu.m to 16 .mu.m. Thus various preventive measures have been taken against spill and leakage of toner from the cartridge.
A conventional toner cartridge is described with reference to the accompanying drawings. FIG. 8 is a side view of an image forming apparatus having a conventional toner cartridge.
In FIG. 8, a photosensitive plate 1 comprises a metal belt made of aluminum and a fine film coated thereon. The fine film functions as a photosensitive receptor and is made of selenium (Se) or organic photocell (OPC). Photosensitive plate 1 is supported by rolls 2, 3 and 4 so that a vertically flat face is formed between rolls 2 and 3. A driving motor (not shown) rotates photosensitive plate 1 on rolls 2 and 3 in a direction shown by arrow "A".
Along the rolling face of photosensitive plate 1, several devices are disposed such as: charger 5; optical exposure system 6; toner cartridges 7B, 7Y 7M, and 7C; intermediate transfer unit 8; photosensitive plate cleaner 9; and decharger 10 in this order along the rolling direction indicated by the arrow "A". In toner cartridges 7B, 7Y, 7M and 7C, developers of respective colors including black (B), yellow (Y), magenta (M), and cyan (C) are stored. Charger 5 comprises charged wires 11 made of tungsten wires, shield plate 12 and grid plate 13 both made of metal plates. A high voltage is applied to charged wires 11 to produce corona discharge, thereby charging photosensitive plate 1 uniformly via grid plate 13.
An exposure-light-beam 14 of image data is emitted from exposure optical system 6. In a case of a laser printer, an exposure light beam 14 is controlled by signals from a host computer (not shown), whereby a plurality of electrostatic latent images, corresponding to the respective colors, are formed on photosensitive plate 1.
Toner cartridges 7B, 7Y, 7M and 7C, corresponding to each color are detachably mounted vertically in this order from top to bottom in a given storage space provided in the apparatus. These cartridges have the same interior arrangement except they include different toners.
FIG. 9 is a perspective view of a conventional cartridge-housing 70 ready to be assembled.
FIG. 10 is a perspective view of a conventional cartridge-cover 71 ready to be assembled.
In FIG. 9, grooves 51a, 51b and 51c are formed on an upper part of side-walls of housing 70.
Sponges 52a, 52b and 52c, pasted with an adhesive agent (e.g., a double faced tape), adhere on grooves 51a, 51b and 51c. On the cover 71 shown in FIG. 10, ribs 53a, 53b and 53c are formed to engage with corresponding grooves 51a, 51b and 51c. Cover 71 is thus tightly mated to housing 70 with sponges 52a, 52b and 52c. Sponge 41 is provided to a toner supply opening in order to prevent the toner from leaking through a gap between the developer roll and cover 71.
In the prior art discussed above, sponges 52a, 52b and 52c are provided to the mating section in order to prevent toner leakage through a gap between housing 70 and cover 71. However, when the apparatus mounted with these cartridges is transported, or when these cartridges are transported independently as supply cartridges, leakage or spillage of toner from the cartridge is still sometimes found due to vibration accompanying the transportation. This happens because the grain sizes of toner ranges from 2 .mu.m to 16 .mu.m (i.e., they are ultra-fine particles when only a non-magnetic material is used).
Installation of pasting sponges 52a, 52b and 52c is cumbersome and time-consuming, because it requires peeling off a release paper from a slip of double-faced tape, and pasting the tape onto narrow grooves 51a, 51b and 51c. This process has significantly lowered operation efficiency.
After the toner cartridges 7B, 7Y, 7M and 7C are replaced, they are supposed to be recycled. Although reusable materials and components are used in the cartridge, the sponges 52a, 52b and 52c with the double-faced tape must be removed. Even when removal is tried, the sponges fray. It is therefore hard to remove the sponges completely from the cartridge and that the discarded cartridge is difficult to be reclaimed. Thus, recycling of the cartridge is hard.